1. Field of the Invention
The present invention relates to an internal pressure adjusting device which adjusts an internal pressure in a fuel tank mounted on the vehicle within a proper range.
2. Description of the Prior Art
Fuel vapor in the fuel tank flows into the in atmosphere from a fuel filler cap where refueling the fuel tank, and pollutes the atmosphere when an upper space in the fuel tank is full of the fuel vapor.
For preventing such air pollution, a canister is provided to adsorb the fuel vapor filled in the upper space of the fuel tank.
Thereafter, the absorbed fuel vapors in the canister are induced in an intake system of an engine through a purge passage to burn in a combustion chamber of the engine when operating the engine.
Heretofore, as to the fuel vapor control system of this type, there has been well known as a prior art technique in the Japanese Patent Application Laid Open Number 202812/1993 by the way of example.
Here, the following is disclosed that a normally opened solenoid valve (pressure control valve) controlled by an electronic control unit is provided in a fuel vapor passage and a duty solenoid valve (purge solenoid valve) controlled by the electronic control unit is mounted on a purge passage. The electronic control unit is provided to control the duty solenoid valve in a duty control responsive to the engine operating conditions to open the purge passage.
As a result, the fuel vapor adsorbed in the canister is purged within the engine intake system through the purge passage.
During this purging, the fuel vapor passage is closed by the closed control of the normal opened solenoid valve only when the internal pressure of the tank is below a predetermined value.
Therefore, a negative pressure in the intake passage of the engine only acts to the canister through the purge passage in the fuel vapor control system during the purging described in the above application.
Therefore, the fuel vapor adsorption ability of the canister is promptly recovered by the reason of that the evaporation fuel adsorbed in the canister is surely purges and induced in the intake passage, to prevent decreasing the fuel vapor adsorption ability without enlarging the canister.
In the fuel vapor control system described in the reference, a large amount of fuel vapor generates in the upper space of the fuel tank while the engine is stopping, because the normally opened pressure control valve mounted on the fuel vapor passage opens at stopping the engine.
In that case, the fuel vapor blows out from the fuel vapor passage to the atmosphere through the canister.
In general, the internal pressure in the fuel tank decreases when the fuel temperature in the tank decreases or the atmospheric pressure rises, at engine operating conditions. As a result, the internal pressure in the tank will be made a negative pressure, before long.
In the fuel vapor control system described in the reference, the negative pressure in the fuel tank decreases more and more by closing the fuel vapor passage and opening the purge passage during executing the purge and operating the fuel vapor control and tended to damage the fuel tank by the excessively decreasing the internal pressure in the fuel tank.